1. Field Of The Invention
This invention relates to a benzoate-phytate corrosion inhibitor system for tinplated steel aerosol containers. It has been discovered that a 0.4 to 1% concentration of 2.5:1 mixture of sodium benzoate and sodium phytate effectively inhibits corrosion of tinplate aerosol cans by hair styling foams which have hitherto been packaged in expensive aluminum aerosol containers and other formulations which are too corrosive to be packaged in unlined tinplated aerosol containers.
2. Description Of The Prior Art
Yamagishi et al., U.S. Pat. No. 3,769,068 relates to a method or process for coating steel plates with aluminum to render the steel plates corrosion resistant. The process includes making a slurry of aluminum powder and water and coating a pretreated steel plate with the slurry to prevent rusting of the underlying steel plate. The aluminum slurry powder is premade and stored for some time before coating. Therefore, there is a possibility that the aluminum powder in the slurry will react with water to make the slurry difficult or impossible to use. To prevent the reaction between the aluminum powder and the water, stabilizing agents including phytic acid are added to the slurry to prevent a chemical reaction between the aluminum and the water and to stabilize the slurry for long periods of time during which it may be stored before coating the steel plate.
In addition, Yamagishi teaches that as a steel strip is fed at slow speeds, under foundry conditions, rust may generate on the strip during the process time between the coating of the steel which the slurry and the final drying of the product. It has been found that this rust is effectively prevented by the addition of a corrosion inhibitor such as sodium nitrite and sodium benzoate. As the steel strip is subject to degreasing with alkali cleaners and water scrubbing whereby oxidation conditions are present, rust can form on the steel plate. The steel plate is also subject to heat in order to rapidly dry the surface and presumably prevent rusting. However, as is well known, surface rust may appear where drying is not complete and indeed, be facilitated in its formation by the application of heat to dry the steel.
Important differences exist between teachings of Yamagishi and the present invention. Specifically, Yamagishi is concerned with the adherence of an aluminum slurry to a steel plate. Moreover, the steel plate itself is treated for rust inhibition while it is heated and under wet conditions so that rust will not form underneath the slurry and impede the adherence of the slurry to the metal plate. In addition, Yamagishi uses phytic acid (instead of its group I metal salt) which we have found does not work as a corrosion inhibitor for tinplate aerosol cans. No mention is made, and none can be seen, of using a sodium phytate and sodium benzoate combination to prevent a corrosive aerosol composition from corroding through a tinplated metal container.
More particularly, it is not seen in Yamagishi to use a specific ratio of sodium phytate and sodium benzoate to prevent a corrosive aerosol composition contained within a tinplated steel container from reacting with exposed metal ions along the seam of the can to prevent failure of the container. Accordingly, the present invention differs from Yamagishi.
Graf. JAOCS, Vol. 60, No. 11 (November, 1983) page 1861 at 1863-65 discloses the use of various salts of phytic acid as corrosion inhibitors on tin plates and cans. Graf states cans treated with phytic acid salts show good oxidation, corrosion and scratch resistance, good solderability, resistance toward blackening by sulfur and superior appearance.
The Graf article does not discuss the synergism of sodium phytate and sodium benzoate in a 2.5:1 ratio to inhibit corrosion of the metal seam of a tin plated steel container by a corrosive aerosol composition. Accordingly, the present invention differs from the Graf articles.